Quantitative MRI methods applied to porous media have the potential to determine a wide variety of valuable petro-physical properties [1]. Most MRI methods feature inherent relaxation time contrast and in many instances this is considered a positive feature. However, core analysis of fluid properties of porous media frequently requires true fluid content images [2].
The SPRITE class of MRI methods have proven to be robust and general in their ability to generate fluid content images [3] in porous media. However, the short encoding times required, with correspondingly high magnetic field gradient strengths and filter widths, and low flip angle RF pulses, yield sub-optimal S/N images, especially at low static field strength.
Spin echo single point imaging (“SE-SPI”) has inherently good S/N due to a relatively narrow signal bandwidth [4]. Lacking magnetic field gradients at the k-space origin, the imaging experiment will not suffer significant diffusive attenuation [5]. In previous work, SE-SPI has proven very successful in cases where the inherent S/N is poor, such as natural abundance 13C imaging [6], 13C gas phase imaging [7] and high resolution thin film imaging [8]. In addition, as a pure phase encoding technique, SE-SPI is largely immune to image distortion due to susceptibility variation and paramagnetic impurities in porous media.
A simple density image of fluid distribution in porous media, with no relaxation time contrast, is remarkably difficult to achieve with conventional methods. Short transverse relaxation lifetimes (T2) yield signal loss while multi exponential T1 and T2 yield variable signal attenuation in a simple spin echo image.